DHukme... as with the four prime disorders I noted each was at one time believed to be unrelated to genetics. Today we know they are genetic based.
Of all human genes mapped to date but half have been purosed. It is somewhere within the other half that those genes that when triggered or other for other inexplicable reasons are caused to express... where it be that those which compel homosexual lust be discovered.
It was also thought that intelligence (aka IQ) was not genetic based. Today we know otherwise and that the Bell Curve of human intellect is both real and genetic based.